287-Find-the-Duplicate-Number.go

func findDuplicate(nums []int) int {
    slow, fast := nums[0], nums[nums[0]]
    
    for slow != fast {
        slow = nums[slow]
        fast = nums[nums[fast]]
    }
    
    slow = 0
    for slow != fast {
        slow = nums[slow]
        fast = nums[fast]
    }
    return slow
}